The present invention relates to metal inert gas robot welders, and more particularly to the wire feed system for such welders. These welders are widely used in assembling electronic packages or modules, which are typically fabricated of aluminum. The aluminum wire electrode which is used for such applications is a small diameter, difficult to handle wire, which must be fed from a wire storage reel to the welding gun, which may be spaced some distance away from the workpiece.
Further background regarding metal inert gas welding, also referred to as gas metal arc welding, and the prior art structures and process parameters can be had from "Welding Handbook" 7th Ed., Vol. 2, pgs. 114-139. In general in a metal inert gas welder, the metal filler electrode is fed as a wire through a welding gun with an inert shielding gas being directed through the wire feed nozzle of the gun about the welding area. The metal filler electrode wire is fed from a supply or storage reel through an electrode guide tube or conduit to the welding gun, with electrical contact to the welding power supply being made to this wire by a current contact tube within the welding gun. A push-pull wire feed or drive mechanism can be located as part of the gun or at the wire supply reel.
Such welders can be automated by mounting the welding gun on a maneuverable robot arm, with the robot controlling the welding operation, and moving the gun over the workpiece in a prescribed path to complete fabrication, of for example, an aluminum chassis, ductwork, heat exchanger housings, or electronic package, all of which are used in radar systems. The robot arm is maneuverable in plural axes, and its positioning of the welding gun at the workpiece must be very accurate, with a computerized control sequence used to align the gun with the workpiece. The workpiece is mounted on a work table which is movable and controlled also by the robot control system. The mounting of the electrode wire storage and feed system upon the robot arm reduces problems associated with feeding small diameter wires over long distances from remotely located storage reels. However, the weight of such wire storage and feed systems, as well as the variation in the weight of the wire stored with time makes it difficult to accurately control positioning of the welding gun by the robot arm.
It is desirable that a constant tension be maintained on the welding gun disposed at the extending end of a robot arm irrespective of movement or position of the robot arm. This will ensure precise controllable alignment of the welding gun with the workpiece.